The present invention relates to multicomponent fibers comprising starch and polymers and specific configurations of the fibers. The fibers are used to make nonwoven webs and disposable articles.
There have been many attempts to make nonwoven articles. However, because of costs, the difficultly in processing, and end-use properties, there are only a limited number of options. Many compositions have limited processability.
Useful fibers for nonwoven article are difficult to produce and pose additional challenges compared to films and laminates. This is because the material and processing characteristics for fibers is much more stringent than for producing films, blow-molding articles, and injection-molding articles. For the production of fibers, the processing time during structure formation is typically much shorter and flow characteristics are more demanding on the material""s physical and rheological characteristics. The local strain rate and shear rate are much greater in fiber production than other processes. Additionally, a homogeneous composition is required for fiber spinning. For spinning very fine fibers, small defects, slight inconsistencies, or non-homogeneity in the melt are not acceptable for a commercially viable process.
Attempts have been made to process natural starch on standard equipment and existing technology known in the plastic industry. Fibers comprising starch are desired as the starch is environmentally degradable. Since natural starch generally has a granular structure, it needs to be xe2x80x9cdestructurizedxe2x80x9d before it can be melt processed into fine denier filaments. Modified starch (alone or as the major component of a blend) has been found to have poor melt extensibility resulting in difficulty in successfully production of fibers, films, foams or the like. Additionally, starch fibers are difficult to spin and are virtually unusable to make nonwovens due to the low tensile strength, stickiness, and the inability to be bonded to form nonwovens.
To produce fibers that have more acceptable processability and end-use properties, thermoplastic polymers need to be combined with starch. Selection of a suitable polymer that is acceptable for blending with starch is challenging. The polymer must have good spinning properties and a suitable melting temperature. The melting temperature must be high enough for end-use stability to prevent melting or structural deformation, but not too high of a melting temperature to be able to be processable with starch without burning the starch. These requirements make selection of a thermoplastic polymer to produce starch-containing multicomponent fibers very difficult.
Consequently, there is a need for a cost-effective and easily processable multicomponent fibers made of natural starches and thermoplastic polymers. Moreover, the starch and polymer composition should be suitable for use in commercially available equipment used to make the multicomponent fibers. There is also a need for disposable, nonwoven articles made from these multicomponent fibers.
The present invention is directed to multicomponent fibers. The configuration of the multicomponent fibers may be side-by-side, sheath-core, segmented pie, islands-in-the-sea, or any combination of configurations. Each component of the fiber will comprise destructurized starch and/or a thermoplastic polymer.
The present invention is also directed to nonwoven webs and disposable articles comprising the multicomponent fibers. The nonwoven webs may also contain other synthetic or natural fibers blended with the multicomponent fibers of the present invention.